Standard head suspension assemblies (HSAs) include, as component elements, a base plate, a load beam, a gimballing flexure and a head slider. The base plate is attached to a proximal end of the load beam, and is configured for mounting the load beam to an actuator arm of a disk drive. The flexure is positioned on a distal end of the load beam. Mounted to the flexure is a head slider, which is thereby supported in read/write orientation with respect to an associated disk.
A conventional flexure, sometimes referred to as a Watrous gimballing flexure design, is formed from a single sheet of material and includes a pair of outer flexible arms about a central aperture and a cross piece extending across and connecting the arms at a distal end of the flexure. A flexure tongue is joined to the cross piece and extends from the cross piece into the aperture. A free end of the tongue is centrally located between the flexible arms. The head slider is mounted to the free end of the flexure tongue.
The head slider must be mounted to the flexure tongue so that the head slider is in a predetermined (e.g., planar and parallel) relationship to the disk surface. During the process of manufacturing and assembling the HSA, any lack of precision in forming or assembling the individual elements contributes to a lack of planarity in the surfaces of the elements. A buildup of such deviations from tolerance limits in the individual elements can cause deviation from desired planar parallelism in the final head suspension assembly. The parameters of static roll and static pitch torque in the final head suspension assembly result from these inherent manufacturing and assembly tolerance buildups.
Ideally, for optimum operation of the disk drive as a whole, during assembly of the head slider to the flexure tongue, the mounting surface datum (to which the load beam is mounted during HSA assembly) and the slider surface datum must be parallel to each other in both planar directions. The mounting surface datum and the slider surface datum are level surfaces used as reference points or surfaces in establishing the planar parallelism of the actuator mounting surface and the head slider surface relative to each other. The upper and lower surfaces of the head slider are also manufactured according to specifications requiring them to be essentially or nominally parallel to each other.
Static roll torque and static pitch torque have their rotational axes about the center of the head slider in perpendicular planar directions, and are caused by unequal forces acting to maintain the desired planar parallelism on the head slider while it is flying over the disk. That is, static torque is defined as a torque or a moment of force tending to cause rotation to a desired static (i.e., reference) attitude about a specific axis.
As applied to a head suspension assembly, the axis of roll torque is coincident with the longitudinal axis of the head suspension assembly. The value of static roll torque is measured on either side of the static roll torque axis when the flexure tongue is parallel with the base plate. If the flexure has been twisted about the static roll torque axis during manufacture (i.e., there is planar non-parallelism of the flexure tongue with respect to the disk along this axis), the values measured on either side of the roll torque axis will not be the same. Thus, when the attached head slider is in flying attitude to the associated disk surface, force (referred to as an induced roll torque value) is needed to twist the tongue back into planar parallel alignment to the disk.
The axis of pitch torque is perpendicular to the longitudinal axis of the head suspension assembly. The value of static pitch torque is measured on either side of the static pitch torque axis when the flexure tongue is parallel with the base plate. If the flexure has been twisted about the static pitch torque axis during manufacture (i.e., there is planar non-parallelism of the flexure tongue with respect to the disk along this axis), the values measured on either side of the pitch torque axis will not be the same. Thus, when the attached head slider is in flying attitude to the associated disk surface, force (referred to as an induced pitch torque value) is needed to twist the tongue back into parallel alignment to the disk. It will of course be understood that in actual conditions the flexure can be twisted with respect to both axes, requiring alignment about both the pitch axis and the roll axis.
These torques can also be referred to in terms of static attitude at the flexure/slider interface and in terms of the pitch and roll stiffness of the flexure. The ideal or desired pitch and roll torques are best defined as those which would exist if the components were installed in an ideal planar parallel configuration in a disk drive. In an actual disk drive, pitch and roll static torques produce adverse forces between the air bearing surface of the slider and the disk, affecting the flying height of the slider above the disk, resulting in deviations from optimum read/write and head/disk interface separation.
In a conventional flexure design, the flexure tongue is offset from the flexure toward the head slider to allow gimballing clearance between the upper surface of the head slider and the lower surface of the flexure. This offset is formed where the flexure tongue and cross piece join, in conjunction with the dimple that is formed on the flexure tongue. This standard flexure design evidences a low value of pitch stiffness and a moderate value of roll stiffness. Pitch stiffness and roll stiffness are each measured in force X distance/degree. Thus, in developing a new design for a flexure, it would be most desirable to provide a flexure and a method of fabrication which accurately compensate and correct for manufacturing variations that currently contribute to static pitch and roll torque errors. The manufacturing process should be efficient to perform corrections for static roll torque, as well as for static pitch torque, since the ability to correct for both static torques is needed for proper flexure/slider alignment.